1. Field of the Invention
The present invention relates to a cylinder-type air damper in which air in air chambers formed in a cylinder is allowed to flow through an orifice as a piston moves relatively in the cylinder, so as to effect damping.
2. Description of the Related Art
As an air damper of this type, for example, one for use in a glove box of an automobile is known.
That is, an air damper is arranged such that an opening in a cylinder is closed by a cap, and a piston rod penetrates the cap and extends outside the cylinder. The piston is provided with an O-ring, and the O-ring is fitted in an annular recess provided on an outer periphery of the piston and abuts against the inner periphery of the cylinder. Two air chambers are respectively formed on both sides of the piston (a first air chamber is formed on the bottom side of the cylinder, and a second air chamber is formed on the opening side of the cylinder).
The piston is provided with an orifice allowing the first air chamber to communicate with the second air chamber.
The recess has such a width as to allow the O-ring to move along the moving direction of the piston. When the piston changes its moving direction from the bottom of the cylinder toward the opening, the O-ring is moved from a second position to a first position by the frictional force between the O-ring and the inner periphery of the cylinder. Conversely, when the piston changes its moving direction from the opening toward the bottom, the O-ring is moved from the first position to the second position by the aforementioned frictional force. A groove is formed in the bottom of the recess, and when the O-ring is at the second position, the first air chamber and the second air chamber communicate with each other through the groove, while when the O-ring is at the first position, the groove is blocked.
When the piston moves toward the opening side of the cylinder, the air flows by means of the orifice, and a damping force operates on the basis of the flow resistance at the orifice. On the other hand, when the piston moves toward the bottom of the cylinder, the air escapes via the groove, and the damping force is reduced
In a case where such an air damper is used in a glove box, the piston rod is connected to a lid of the glove box, and the cylinder is connected to the accommodating side of the glove box. When the lid is opened, the piston rod is drawn out through the cylinder, so that the piston moves from the bottom of the cylinder toward the opening. Consequently, when the lid is opened, the opening motion is made slow so as not to cause a shock. On the other hand, when the lid closed, the closing motion is becomes faster.
In a case where the lid of the glove box is opened from a vertical state toward a horizontal state, the load applied to the lid becomes gradually greater (the load changes) as the lid is opened, so that the lid-opening speed becomes faster. Accordingly, as the lid approaches the position of this opening limit, the damping force caused by the air damper becomes insufficient. At the position of the opening limit of the lid, the lid sometimes bounds, so that a smooth opening motion cannot be obtained.
Meanwhile, if the damping force of the air damper acts during an initial period of the opening motion of the lid, it is conceivable that the lid may possibly remain in the vertical state and may not open.